By itself, you likely do not have SIP capabilities, but you can do so if you are willing to spend money and/or have an Android or iPhone. In on themselves, they do not have it, but that is what the respective application store is for. You could also go another route, and acquire either an ATA and plug your old touch tone POTS phone into the ATA, or acquire a SIP phone. Personally, I use a Grandstream WP825, but at time of writing this, it was $120. This might be a big pill to swallow, but I never looked back regretting my decision. Still, I can understand that if something is unaffordable it doesn’t matter if it is $120, or $120,000.
SIP Client
There are multiple options for SIP clients. You would want to download from a reputable developer. Installing a “SIP” client that may be malware will make this effort not worth it. I personally used Acrobits SIP client, however this was a $10USD purchase. If you are on a tight budget, this might not be feasible. I have heard good things of 3CX’s SIP client, and 3CX is a reputable company. I would consider them if you want free. You would be limited to 2 SIP accounts if I remember correctly. I never installed 3CX, so I can’t tell you the performance of 3CX.
SIP Phone
There are so many options. Again, if you choose an ATA, you will then be able to plug in any old phone that is not a rotary telephone. ATAs and rotary phones don’t play well together. However, if you have a rotary phone that still works – kudos to you! Acquiring a SIP phone might be cheaper than acquiring a smartphone. If you want this to function as a home phone, then a SIP phone is your best option. If you install a SIP client onto your smartphone, then your SIP client will ring when you aren’t in a wifi network, and therefore can consume your cellular data. This might be fine for many, but especially those in developing countries will likely not have an unlimited, or even reliable cellular data. If you live in such a country, I am sure you already know these issues. However, if you chose to use a SIP phone, keep in mind you will need home internet services. You would plug the ATA into one of the RJ45-LAN ports, or better yet, you acquired a Wifi Phone, and will setup to connect to the Wifi once you receive the phone.